Linux: Use After Free
CVE-2024-26996 is a high-severity use after free vulnerability in Linux, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists versions 7f67c2020cb08499c400abf0fc32c65e4d9a09ca, 0588bbbd718a8130b98c54518f1e0b569ce60a93, f356fd0cbd9c9cbd0854657a80d1608d0d732db3 as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.24% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Linux to 7f67c2020cb08499c400abf0fc32c65e4d9a09ca or 0588bbbd718a8130b98c54518f1e0b569ce60a93 or f356fd0cbd9c9cbd0854657a80d1608d0d732db3 or 7250326cbb1f4f90391ac511a126b936cefb5bb7, whichever matches your release line, or a later version.
- Update Linux Kernel to 5.15.157 or 6.1.88 or 6.6.29 or 6.8.8, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 6b4012a2e4d4702f8fb0ee1db1c0f0b17ab7d41b up to, but not including, 7f67c2020cb08499c400abf0fc32c65e4d9a09ca; 6b4012a2e4d4702f8fb0ee1db1c0f0b17ab7d41b up to, but not including, 0588bbbd718a8130b98c54518f1e0b569ce60a93; 6b4012a2e4d4702f8fb0ee1db1c0f0b17ab7d41b up to, but not including, f356fd0cbd9c9cbd0854657a80d1608d0d732db3; 6b4012a2e4d4702f8fb0ee1db1c0f0b17ab7d41b up to, but not including, 7250326cbb1f4f90391ac511a126b936cefb5bb7; 6b4012a2e4d4702f8fb0ee1db1c0f0b17ab7d41b up to, but not including, 6334b8e4553cc69f51e383c9de545082213d785e; 4.4 | 7f67c2020cb08499c400abf0fc32c65e4d9a09ca, 0588bbbd718a8130b98c54518f1e0b569ce60a93, f356fd0cbd9c9cbd0854657a80d1608d0d732db3, 7250326cbb1f4f90391ac511a126b936cefb5bb7, 6334b8e4553cc69f51e383c9de545082213d785e |
| Linux | Linux Kernel | before 5.15.157; 5.16 up to, but not including, 6.1.88; 6.2 up to, but not including, 6.6.29; 6.7 up to, but not including, 6.8.8; 6.9 | 5.15.157, 6.1.88, 6.6.29, 6.8.8 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- LocalThe attacker needs local access or must trick a user into running something.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.8 | High | CNA |
| CVSS 3.1 | 7.8 | High | NVD |
Official description
In the Linux kernel, the following vulnerability has been resolved: usb: gadget: f_ncm: Fix UAF ncm object at re-bind after usb ep transport error When ncm function is working and then stop usb0 interface for link down, eth_stop() is called. At this piont, accidentally if usb transport error should happen in usb_ep_enable(), 'in_ep' and/or 'out_ep' may not be enabled. After that, ncm_disable() is called to disable for ncm unbind but gether_disconnect() is never called since 'in_ep' is not enabled. As the result, ncm object is released in ncm unbind but 'dev->port_usb' associated to 'ncm->port' is not NULL. And when ncm bind again to recover netdev, ncm object is reallocated but usb0 interface is already associated to previous released ncm object. Therefore, once usb0 interface is up and eth_start_xmit() is called, released ncm object is dereferrenced and it might cause use-after-free memory. [function unlink via configfs] usb0: eth_stop dev->port_usb=ffffff9b179c3200 --> error happens in usb_ep_enable(). NCM: ncm_disable: ncm=ffffff9b179c3200 --> no gether_disconnect() since ncm->port.in_ep->enabled is false. NCM: ncm_unbind: ncm unbind ncm=ffffff9b179c3200 NCM: ncm_free: ncm free ncm=ffffff9b179c3200 <-- released ncm [function link via configfs] NCM: ncm_alloc: ncm alloc ncm=ffffff9ac4f8a000 NCM: ncm_bind: ncm bind ncm=ffffff9ac4f8a000 NCM: ncm_set_alt: ncm=ffffff9ac4f8a000 alt=0 usb0: eth_open dev->port_usb=ffffff9b179c3200 <-- previous released ncm usb0: eth_start dev->port_usb=ffffff9b179c3200 <-- eth_start_xmit() --> dev->wrap() Unable to handle kernel paging request at virtual address dead00000000014f This patch addresses the issue by checking if 'ncm->netdev' is not NULL at ncm_disable() to call gether_disconnect() to deassociate 'dev->port_usb'. It's more reasonable to check 'ncm->netdev' to call gether_connect/disconnect rather than check 'ncm->port.in_ep->enabled' since it might not be enabled but the gether connection might be established.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use After Free
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.
How developers prevent this class of flaw
- Choose a language that provides automatic memory management.
- When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- git.kernel.org/stable/c/0588bbbd718a8130b98c54518f1e0b569ce60a93
- git.kernel.org/stable/c/6334b8e4553cc69f51e383c9de545082213d785e
- git.kernel.org/stable/c/7250326cbb1f4f90391ac511a126b936cefb5bb7
- git.kernel.org/stable/c/7f67c2020cb08499c400abf0fc32c65e4d9a09ca
- git.kernel.org/stable/c/f356fd0cbd9c9cbd0854657a80d1608d0d732db3
Other references
Recent Use After Free vulnerabilities
- 9.8 Critical severity
- 8.8 High severity
- 8.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
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